The present invention relates to a lithography system for projecting an image pattern onto a target surface such as a wafer, wherein control data are coupled to a control unit for controlling exposure projections by means of light signals, using a free space interconnect. The present invention relates in particular to a system wherein such control unit is included in close proximity to or within the projection space, more in particular to a multi-beam mask-less lithography system. The current invention in principle relates all the same to charged particle and to light projection based lithography systems
Such a system is known, e.g. from the international patent publication WO2004038509 in the name of Applicant, i.e. from the particular embodiment provided by FIG. 14 thereof. The known system comprises a computer system for providing pattern data of an image to be projected by a so called beam column for projecting charged particles, in particular electrons on to a target surface such as a wafer and an inspection tool. The beam column comprises a vacuum chamber in which one or more charged particle sources are accommodated, which emit particles in a manner known per se, using amongst others an electric field for withdrawing particles from said source or sources.
The beam column further comprises charged particle optic means for converging an emitted bundle of charged particles, for splitting up the same into a multiplicity of charged particle beams, further referred to as writing beams, and forming exposure projections. A control unit for controlling the exposure projections is included in the form of charged particle optical means for shaping or directing such writing beams, here showing a blanker optical part or modulator array comprising blanking deflectors, as well as a writing deflector array for deflecting writing beams for the purpose writing of a pattern using writing beams not blanked by said blanking deflectors.
The blanker optic part, known per se, e.g. from international patent publication WO2004107050 in the name of Applicant, deflects, depending on a computer provided signal a writing beam away from a straight trajectory parallel with other writing beams, to such amount of inclination that no part of the writing beam effectively passes the opening provided for each writing beam in a stopping plate, thereby effecting an “off” state of the particular writing beam.
All optic parts in the beam column are shaped with an array of openings, the openings of the separate parts being mutually aligned so as to enable the passage of a writing beam in said column towards said target surface in a controlled manner. The known mask-less multi-beam system is further typically provided with blanking deflectors having both the source and the target surface arranged in a conjugate plane thereof, i.e. it may easily be combined with the subject matter of WO2004/0819010. In this manner the lithography system favorably realizes an optimal brightness of the source on the target surface. Also, in this manner a minimum amount of space is required for the blanker array.
The target surface for a writing beam is held on a stage included in the beam column. The stage, induced by an electronic control unit of the system, moves together with said surface perpendicularly relative to said emitted writing bundles, preferably solely in a direction transverse to a direction in which such writing bundles are finally deflected for writing purposes. Writing of a pattern by the known lithography system is thus effected by the combination of relative movement of the target surface and a timed “on” and “off” switching of a writing beam by said blanker optics upon signaling by said control unit, more in particular by a so-called pattern streamer thereof.
Signaling for on/off switching, i.e. modulating of a writing beam is in the related known system performed by using light optics. The blanker optics thereto comprises light sensitive parts such as photodiodes, for receiving light signals, which are converted into electronic signals, e.g. applying the measures as provided by the international patent publication WO2005010618 in the name of Applicant. The light signals are produced by electronic to light conversion by said control unit for the system, and are transported to the beam column by means of an optical carrier, in casu a bundle of glass fibers that finally projects from “e.g. a transparent part of the vacuum boundary”. Light signals are projected to said blanker optics using a lens system, which in the known system is disclosed to be comprised of a converging lens located in between a transmitter part and the light sensitive parts of deflectors included in the blanker optic part. The arrangement of deflector, light sensitive parts and light to electric conversion is produced using both so-called MEMS- and (Bi-) CMOS-technology. So as to prevent the use of mirroring parts, in the related known system the signaling light beams are projected from a far upper side relative to the blanking optic part, so as to achieve an angle of incidence of the pattern information carrying light signals on the light sensitive elements, as small as possible. The publication in which the related embodiment is comprised, teaches however, that other locations of projection may be realized when using mirrors for correcting the larger angles of incidence occurring at most of such alternative locations.
Although general set up of the above described lithography system has proven to be satisfactory, drawbacks are noticed at the oblique illumination system disclosed, in that it suffers from non-optimal transmission of light, at least less than expected and in that it suffers from relatively large aberrations. The present invention therefore seeks to improve the known mask-less multi-beam lithography system in general, however, in particular as to the light optics system (LOS) thereof. The present invention further has for an object to improve the lithography system by either increasing the light transmission efficiency thereof and/or by reducing the chance of aberrations in the light optic part thereof.